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  • 學位論文

聚對位苯基乙烯衍生物及其摻合物靜電紡絲發光奈米纖維之製備、 形態及光物理特性研究

Morphology and Photophysical Properties of Light-Emitting Electrospun Nanofibers Prepared from Poly(p-phenylene vinylene) (PPVs) Derivatives and Polymer Blends

指導教授 : 陳文章

摘要


共軛高分子由於具有非常顯著的電子及光電特性,已廣泛地應用於多元的電子及光電元件上。共軛高分子的光物理性質可以經由合適的高分子共聚物或高分子混摻之方法調控。然而,目前的研究多是以共軛高分子薄膜的形態為主。由於靜電紡絲低成本優勢、可撓式形態調控以及高連續生產率過程,使得靜電紡絲成為一種新的技術生產各式各樣的功能性奈米纖維。共軛高分子奈米纖維的導電度、場效遷移率或光致發光等性質相較於共軛高分子薄膜而言具有非常顯著的不同,此乃因不同的幾何侷限所導致。在此論文中利用聚對位苯基乙烯衍生物及其摻合物製備出不同樣式的共軛高分子靜電紡絲奈米纖維(包含不織布、核殼型及定向性),研究靜電紡絲纖維的形態與光物理特性以及靜電紡絲纖維與混摻成分之關連性,概括如下: 在第二章,我們證實DB-PPV奈米纖維可以利用同軸靜電紡絲方式製造出來,其中DB-PPV(核層)溶於氯苯或氯仿中;而PVP(殼層)溶於水與酒精的混合溶劑中。由於溶劑的擴散速率明顯比靜電紡絲過程慢,因而這類核-殼形態的奈米纖維可以經由同軸靜電紡絲方式成功地保存下來。當洗去外層的PVP之後,就可以得到具有定向ribbon-like皺紋表面的純DB-PPV奈米纖維,而定向性ribbon-like皺紋表面是因為萃洗過程所致。調控內部DB-PPV溶液的流速從0.15到0.6 ml/h,會導致整個核-殼纖維的平均尺寸的增加,使得DB-PPV/PVP纖維平均尺寸從580 nm微幅增加至633 nm,而內層DB-PPV的體積分率亦會隨著流速增加而有相同增大趨勢。此外可由Rayleigh 方程式和Fowler-Nordheim 理論搭配靜電紡絲不同製程參數之調控來預測纖維尺寸大小。純DB-PPV靜電紡絲奈米纖維的UV-vis最大吸收峰位置會因為由氯苯或氯仿溶劑系統製備而有所不同。在氯苯最大吸收峰位置在454 nm (λabsmax = 454 nm),而在氯仿系統最大吸收峰位置則些微紅移至458 nm (λabsmax = 458 nm)。這可以用氯仿、氯苯及DB-PPV的溶解度參數不同來解釋。從氯仿及氯苯溶劑系統所製備出的DB-PPV靜電紡絲奈米纖維的PL光譜與UV-vis吸收光譜具有相同的趨勢。此外,不論是由氯苯或氯仿溶劑系統所製備的DB-PPV靜電紡絲奈米纖維都比其相對應條件下的薄膜來的紅移。此意味著DB-PPV靜電紡絲纖維內部的分子鏈具有較佳的順向性排列並導致π-共軛程度的改善。研究結果顯示經由同軸靜電紡絲方式可以成功地製備共軛高分子靜電紡絲纖維包含核-殼型奈米纖維。 在第三章,利用單軸靜電紡絲系統,成功地製備出DB-PPV混摻非共軛高分子(聚甲基丙稀酸甲酯,PMMA)之二元混摻靜電紡絲纖維。DB-PPV/PMMA混摻發光靜電紡絲纖維的形態及光物理性質可以經由調控不同的溶劑及DB-PPV之含量而有非常顯著的不同。由於氯仿、四氫呋喃及氯苯三種溶劑沸點不同導致DB-PPV/PMMA混摻纖維表面呈現孔洞、皺紋及平滑三種形態,並且致使纖維內部DB-PPV不同程度的聚集形態。經由TEM觀察在氯仿及四氫呋喃的溶劑系統中,發現二元混摻纖維中的DB-PPV組成傾向以核-殼型結構方式自我聚集(core-shell structure, 60-70 nm);相較於氯苯溶劑系統中,纖維中的DB-PPV傾向以線狀結構自我聚集(wire-like structure, 10-20 nm)。UV-vis吸收波長或光激發光波長的最大峰(absorption or luminescence spectra)會隨著較多的DB-PPV聚集尺寸或DB-PPV混摻比例增加而發生紅移現象,但發光量子效率則呈現相反趨勢。此外,搭配自製的矩形收集器,可以得到定向性靜電紡絲奈米纖維。高度定向性的發光DB-PPV/PMMA混摻靜電紡絲纖維於氯苯溶劑系統再搭配自製的矩形收集器成功地製造。隨著DB-PPV/PMMA混摻比例從1 wt%增加至30 wt%會使偏極綠光效果 (dichroic ratio) 從1.58倍提升至3.20倍之多。除此之外,定向性纖維的偏極光強度比不織布及薄膜更勝許多。因此可以藉由溶劑種類選擇及共軛高分子混摻比例不同來調控靜電紡絲奈米纖維的形態及光物理特性。 在第四章,利用單軸靜電紡絲方法將PFO/MEH-PPV/PMMA於氯仿溶劑系統中,製備三元混摻發光靜電紡絲奈米纖維。將PMMA重量百分率固定在90 wt%,探討PFO/MEH-PPV混摻比率變化對纖維形態及光物理特性之影響。使用場發射電子顯微鏡與螢光顯微鏡觀察靜電紡絲纖維的形態,發現所得的靜電紡絲纖維平均尺寸大約是數百個奈米左右,且纖維表面具有30-35 nm大小的孔洞。調控PFO/MEH-PPV混摻比率,更可進一步製備出新穎的全彩發光靜電紡絲奈米纖維。PFO/MEH-PPV/PMMA三元混摻奈米纖維發光顏色隨著MEH-PPV組成增加而從藍色變成白色、黃綠色、綠黃色、橘色最後轉變成黃色。與相同混摻組成比率的薄膜進行比較,發現其發光顏色隨著MEH-PPV組成增加而從藍色變成橘色、粉紅色、紅色、最後轉變成深紅色。根據溶解度參數,PFO和MEH-PPV彼此可以互溶並且被侷限在PMMA母相中。因此在這兩個高分子間的能量轉移是有機會發生的。相較於薄膜而言,靜電紡絲奈米纖維中較小尺度的聚集會降低能量轉移效率而導致纖維具有不同光色的變化。另外,靜電紡絲奈米纖維相較於薄膜而言具有更高的發光量子效率。當PFO/MEH-PPV/PMMA三元混摻比例調控在9.5/0.5/90時,可以得到純白發光靜電紡絲奈米纖維,其CIE座標在(0.33, 0.31)。我們的結果顯示經由調控PFO和MEH-PPV兩者共軛高分子在透明基材PMMA中的混摻組成比率可以得到不同顏色的發光靜電紡絲纖維。 本論文研究結果證實經由操控混摻成分、溶劑種類以及收集器不同可以得到不同形態的共軛高分子靜電紡絲纖維。此外,發光特性可以經由能量轉移及不同共軛官能基混摻比例而有效地改變。這類的靜電紡絲奈米纖維具有相當大的潛力應用於新型光源或智慧型紡織品的感測材料之領域。

並列摘要


Conjugated polymers have been extensively studied for diverse electronic and optoelectronic devices due to the excellent electronic and optoelectronic properties. The photophysical properties of conjugated polymers could be tuned through the approaches of copolymers, or blending. However, most of the above studies are based on the thin film devices. Electrospinning (ES) has emerged as a new technique to produce various functional nanofibers because of its advantages of low cost, flexible morphology tuning, and a high-throughput continuous production process. The electrical conductivity, field effect mobility, or photoluminescence of the conjugated polymer ES nanofibers were found to be significantly different from those of spin-cast films due to different geometry confinement. In this dissertation, various ES nanofibers (nonwoven, core-shell type, and aligned) were prepared from poly(p-phenylene vinylene) derivatives and their polymer blends. The morphology and photophysical properties of the prepared ES nanofibers were characterized and correlated with the blend compositions, as summarized below: In Chapter 2, 2,3-dibutoxy-1,4- poly(phenylene vinylene)(DB-PPV) nanofibers were fabricated by coaxial electrospinning DB-PPV (core) in chlorobenzene or chloroform and PVP (shell) in water and ethanol mixture. The diffusion rates of solvents were significantly slower than that in the electrospinning process and thus the core-shell morphology was preserved through the process. After the removal of PVP, the resulting DB-PPV fibers were obtained as a ribbon-like structure aligned with wrinkled surface due to the extraction process. By adjusting the inner flow rates from 0.15 to 0.6 ml/h led to increase the overall average diameter of DB-PPV/PVP nanofibers from ca. 580 to 633 nm, while the core volume fractions also followed the same trend. Also, the fiber diameters studied as a function of various ES parameters could be predicted by the Rayleigh equation and Fowler-Nordheim theory. Different UV-vis absorption peak maxima of DB-PPV nanofibers prepared from CB (λabsmax = 454 nm) and CHCl3 (λabsmax = 458 nm) were observed, which were explained by the polymer solubility in two solvents. The photoluminescence spectra of the ES fibers from the two solvent exhibited a similar trend as the absorption. Moreover, Pure DB-PPV ES fibers prepared from either CB or CHCl3 solvent systems showed a slightly red-shifted as compared to corresponding spin-coated films, which could be due to the better chain alignment and lead to improved

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